Speaker
Description
Many-body perturbation theory methods are able to accurately predict quasiparticle (QP) and spectroscopic properties of several classes of materials. However, the calculation of the QP band structure of 2D materials is known to require a very dense BZ sampling. For 2D semiconductors, large q-point grids are required to describe the sharp q-dependence of the dielectric matrix in the long-wavelength limit (q $\rightarrow$ 0).
In this talk, I will first describe a new methodology able to drastically improve the convergence of the QP corrections in 2D semiconductors with respect to the BZ sampling by combining a Monte Carlo integration method with an interpolation scheme able to describe the sharp dispersion of the dielectric function. Then, I will show how to integrate the new methodology with a multi-pole expansion of the frequency dependence of the screening, able to reach the accuracy of full-frequency methods with a coarse sampling of the frequency space. The combined approach will be used to obtain accurate results for graphene QP band structure. The latter is finally used to calculate electron energy loss spectra (EELS) of graphene at finite momentum transfer via the Bethe-Salpeter equation (BSE), showing excellent agreement with recent high-resolution experimental data, provided that the electron-hole interaction is properly taken into account.
